All of the mobile photos you see here on my site are taken with an Apple iPhone and then emailed to my Web site for publishing. It appears that Flickr users are also using their iPhone's to upload photos to the Web.
As of: May 1, 2008
Somewhat recently, according to this graph (pictured), the Apple iPhone has taken over the top spot as Flickr user's use it more than any other camera phone to publish photos to Flickr. The Nokia N95 had a demanding lead over every other camera phone, while the iPhone took the lead with an amazing upswing.
This is not suprising to me, giving the ease of uploading from the iPhone to Flickr through email. For those that have "jail broken" their iPhones there is also an application they can use to upload photos directly to Flickr. I shutter [sic] to think what this graph will look like once version 2 of the iPhone software comes out, and there is an official application, or many applications, for uploading photos to Flickr.
Source: Flickr: Camera Finder.